1. Field of the Invention
This invention relates to thumbwheel switches, and more particularly, to an electronic thumbwheel switch operable under supervisory control.
2. Background of the Invention
Process control systems and other industrial control systems typically utilize numeric values as set points and as input parameters, for example, to control the overall system. Therefore, any apparatus used for determining such numeric values is of major importance to both the system end-user and the system designer. Criteria involved in the selection of such apparatus include cost, ease of use, reliability and flexibility.
One known device for generating a numeric input value comprises a thumbwheel switch. Such a known thumbwheel switch comprises a numbered cylinder having a user rotatable drive mechanism for selecting the number for display. Particularly, the cylinder may be rotated by a finger, such as a thumb, and thus the name thumbwheel. The rotational position of the cylinder controls a series of switch contacts which are electrically coupled to a plurality of switch terminals. These switch terminals can be connected to an external control device which senses the status of the switches to determine the displayed numeric value.
The use of such prior electro-mechanical thumbwheel switches has proven costly and cumbersome to implement in an overall control system. Specifically, each thumbwheel switch typically requires two or three connectors, necessary cable, pullup resistors and multiplexer logic to determine the numeric value. Also, such thumbwheel switches are inflexible in their application and do not lend themselves to microprocessor and microcontroller based systems. In fact, such devices are intended more specifically for use in hard wired systems.
Prior control systems often required the use of numerous thumbwheel switches, with each switch serving a dedicated function. The requirement for such a vast number of switches adds significant cost not only for the actual hardware, but the extra switches require additional panel space as well as labor costs for wiring the same to the control devices.
The present invention is intended to overcome one or more of the problems as set forth above.